1) Field of the Invention
The present invention relates to a composite magnetic member comprising at least one non-magnetized part and at least one ferromagnetized part, both parts being continuously and integrally formed, a process for producing the member and an electromagnetic valve using the member, and particularly to a composite magnetic member capable of fully maintaining ferromagnetic and non-magnetic characteristics against changes in temperature, a process for producing the member and an electromagnetic valve using the member.
2) Description of the Related Art
In generating a magnetic circuit in products such as electromagnetic valves, etc. by discretely providing a ferromagnetic part and a non-magnetic part in one product, it is necessary to make a mild steel part from a ferromagnetic material and an austenitic stainless steel part from a non-magnetic material individually, then assemble the ferromagnetic part and the non-magnetic part together while joining the parts properly by bonding, for example, by soldering, to make a member for the magnetic circuit. However, in making a member for the magnetic circuit in this manner, it is necessary to make a plurality of parts from a ferromagnetic material and a plurality of parts from a non-magnetic material individually and assemble such pluralities of the parts, while joining them by bonding. Thus, many steps and much labor are required for making such a member, complicating the procedure.
It is known that ordinary austenite stainless steel, high manganese steel, etc. are in a non-magnetic state after solid-solution treatment, but can be given a ferromagnetic property by cold working at room temperature to induce and generate a martensite structure. However, the degree of ferromagnetization obtained by this procedure is not high and thus it is actually difficult to apply this procedure to the production of members for the magnetic circuit.
It is also possible as a means for locally non-magnetizing part of a ferromagnetic material such as mild steel, etc. to diffuse an austenitizing element such as Mn, Cr, Ni, etc. into the ferromagnetic material from the surface, but such a means still has a problem in the production of members for the magnetic circuit.
JP-A-63-161146 discloses materials utilizable as a magnetic scale by optimizing the composition of austenite stainless steel or high manganese steel and working procedures for such materials to make members having both ferromagnetic and non-magnetic properties at the same time, where metastable austenite stainless steel is cold drawn into wires, thereby ferromagnetizing the austenite stainless steel based on martensitizing of austenite structure and part of the martensitized wires are further subjected to a local solid-solution treatment to locally non-magnetize the martensitized wires on the basis of local back-austenitization. Members having both ferromagnetic and non-magnetic properties at the same time can be obtained thereby. In this case, the composite magnetic members disclosed in JP-A-63-161146 can have a satisfactorily ferromagnetized part and a satisfactorily non-magnetized part, as integrated together, which can work satisfactorily under the ordinary circumstances, but no measures have been taken against temperatures at which the non-magnetized parts are to be used. That is, under severe temperature circumstance such as an extremely low temperature circumstance, a martensite structure is generated on the non-magnetized part, thereby transforming the non-magnetic properties to ferromagnetic properties. This has been a problem.
Currently available electromagnetic valves work as follows: a magnetic circuit is generated by passing an electric current through a coil in the valve, and a plunger is actuated through a sleeve undergoing magnetic working by the generated magnetic circuit. Particularly when an electromagnetic valve is used for oil-hydraulic control, the plunger must slide oil-tight along the inside surface of the sleeve. The conventional sleeve is made from a non-magnetic material, and to make the plunger behavior more sensitive, the magnetic circuit must be permeated through the non-magnetic material, and thus the force of excitation of the coil itself must be increased. Still furthermore, it is possible to ferromagnetize only part of the sleeve through which the magnetic circuit is to permeate. In the sleeve structure made by integrating a plurality of parts by bonding, the bonding must be carried out by soldering, welding, or the like to make the sleeve, and thus considerable post-working is required for obtaining desired dimension, shape and precision. Thus, there is a post-working problem.
An object of the present invention is to provide a composite magnetic member comprising at least one satisfactorily ferromagnetized part and at least one satisfactorily non-magnetized part, both parts being continuously and integrally formed, which can work under severe circumstances such as an extremely low temperatures; a process for producing the member; and an electromagnetic member using the member.
At first, the present inventors have carefully checked what physical characteristics are desirable for a composite magnetic member having satisfactory ferromagnetic and non-magnetic characteristics at the same time under ordinary circumstances, and have found that a composite magnetic member is required to comprise a non-magnetized part having a relative magnetic permeability xcexc of not more than 1.2 and the remaining ferromagnetized part having a magnetic flux density B50 of not less than 0.3 T at the same time except at the transition region between the non-magnetized part and the ferromagnetized part and except parts particularly not required for the ferromagnetic characteristics.
To satisfy the above-mentioned requirements, the present inventors have selected the following composition which can generate a stable austenite structure at room temperature and also generate a martensite structure by cold working to make the cold worked parts ferromagnetic and can give satisfactory magnetic characteristics.
A metallic member that can meet the above-mentioned requirements has a composition which comprises not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% Mo, not more than 1% Nb, and the balance being Fe and inevitable impurities, where it is desirable that:
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19%, wherein % is and will be hereinafter by weight.
As to Hirayama""s equivalent, reference is made to Nihon Kinzoku Gakkaishi (Journal of the Society of Metallurgy of Japan), 34 No. 5, 507-510 (1970); 34 No. 8, 826-829 (1970); 34 No. 8, 830-835 (1970); 35 No. 5, 447-451 (1971).
The C content is selected to be not more than 0.6% in the above-mentioned composition of the metallic member because shapability by working is lowered with increasing carbide content, though the magnetic characteristics can be satisfied over 0.6% C. The Cr content is selected to be 12 to 19% and the Ni content to be 6 to 12%, Since non-magnetic properties, for example, a relative magnetic permeability xcexc of not more than 1.2, cannot be obtained below the lower limit Cr and Ni contents, whereas above the higher limit Cr and Ni contents, B4000, a magnetic flux density when the intensity of magnetic field is 3.980 A/m, cannot be made less than 0.3 T (0.3 tesla). When the Mn content is over 2%, the shapability by working is lowered. Thus, the upper limit Mn content is selected to be 2%.
Furthermore, specific amounts of Mo and Nb can be contained in the metallic member. Mo, when contained, can effectively lower a Ms point, and Nb, when contained, can effectively contribute to an increase in the strength of the metallic member. Mo or Nb or both Mo and Nb can be contained, depending on the desired purpose. It is preferable that the metallic member contains not more than 2% Mo and not more than 1% Nb. Above these upper limit contents the shapability by working will be lowered.
Limitation of the respective elements to the above-mentioned ranges is still not satisfactory, and it is necessary that desired magnetic characteristics be obtained by combinations within these combination ranges. To this effect, Hirayama""s equivalent H eq=20-23%, nickel equivalent Ni eq=9-12% and chromium equivalent Cr eq=16-19% must be satisfied in the present invention. Unless these conditions are not satisfied, only one of desired ferromagnetic characteristics and desired non-magnetic characteristics is satisfied.
Grounds for specifying these conditions will be explained below:
FIG. 1 shows a relationship between a Hirayama""s equivalent and a relative magnetic permeability.
As is apparent from FIG. 1, a relative magnetic permeability xcexc is lowered with increasing Hirayama""s equivalent H eq, and when the Hirayama""s equivalent H eq is not less than 20%, a relative magnetic permeability xcexc of not more than 1.2 can be satisfied. Thus, the lower limit to the Hirayama""s equivalent H eq is selected to be 20%.
FIG. 2 shows a relationship between a draft percentage at cold working and a magnetic flux density B4000 after the cold working.
As is apparent from FIG. 2, the austenite structure is stabilized with increasing Hirayama""s equivalent H eq, and as a result ferromagnetization by cold working is hard to take place and the magnetic flux density B4000 is lowered. At the cold rolling as cold working, B4000=0.3 T was hard to obtain over H eq=23%, even if the draft percentage was increased. Thus, the upper limit to Hirayama""s equivalent H eq is selected to be 23% in the present invention.
A nickel equivalent Ni eq and a chromium equivalent Cr eq are selected to be 9-12% and 16-19%, respectively, for the same reasons as above.
Usually not more than 2% Si and not more than, 0.5% Al as deoxidizing elements and other inevitable impurity elements are contained in the metallic member, but these elements will not give any adverse effect on the characteristics of the composite magnetic member, when produced.
The present inventors have further found that the metallic member having the above-mentioned composition did not have satisfactory magnetic characteristics under severe temperatures, and have made a further extensive study. That is, the present inventors made metallic members satisfying the above-mentioned conditions for the composition and subjected the members to solid-solution treatment to non-magnetize them, and then left them to stand at various low temperatures. As shown in FIG. 3, an increase in the relative magnetic permeability was observed in the members and the requirements of xcexc=not more than 1.2 as the non-magnetic characteristics were not satisfied.
Thus, it has been found further necessary that the metallic members having the above-mentioned composition satisfy the requirements for ferromagnetic and non-magnetic characteristics at the same time and undergo no change in the relative magnetic permeability xcexc of the non-magnetized part even under a severe temperature circumstance.
As a result of further extensive studies, the present inventors have found metal member structures without any change in the relative magnetic permeability xcexc even at an extremely low temperature, such as a temperature as low as xe2x88x9240xc2x0 C. That is, the present inventors have found that an increase in the relative magnetic permeability xcexc at an extremely low temperature is due to a fact that the extremely low temperature is lower than an Ms point temperature, i.e. a temperature that initiates to transform the austenite structure to the martensite structure, and have conceived that an increase in the relative magnetic permeability at a temperature as low as xe2x88x9240xc2x0 C. can be suppressed by making the Ms point temperatures of the metallic members having the above-mentioned composition lower than, for example, xe2x88x9240xc2x0 C.
Thus, the present invention is characterized by changing grain sizes of austenite crystal grains to make the Ms point temperature lower than the conventional Ms point temperature, thereby suppressing changing of the non-magnetic characteristics to the ferromagnetic characteristics in an extremely low temperature circumstance. That is, the present invention has applied to the composite magnetic members for the first time the following fact the Ms point temperature that initiates to transform the austenite structure to the martensite structure is lowered be decreasing austenite crystal grain sizes.
FIG. 4 shows a conceptual diagram showing the above-mentioned fact. As is apparent from FIG. 4, the austenite crystal grain sizes and the Ms point temperature are closely related each other and the Ms point temperature is abruptly lowered at a specific crystal grain size.
FIG. 5 shows changes in the relative magnetic permeability xcexc of metallic member before cooling and after being cooled to and retained at xe2x88x9240xc2x0 C. for one hour. As is apparent from FIG. 5, the present inventors have found for the first time that the relative magnetic permeability xcexc will not exceed 1.2, even when the metallic members is kept at xe2x88x9240xc2x0 C. by selecting heating conditions so that the austenite crystal grain size is kept not more than 30 xcexcm.
The present inventors have furthermore studied an optimum process for making the crystal grain size of austenite part (non-magnetized part) of the metallic member not more than 30 xcexcm, and have found that the optimum process comprises subjecting the metallic member to cold working, thereby ferromagnetizing the member and then to solid-solution treatment within 10 seconds. That is, the heating of the member must be carried out for a very short time. An increase in the grain size in the region of the member, where the martensite structure is transformed to the austenite structure, can be prevented by conducting the solid-solution treatment within 10 seconds. To this effect, specifically it is desirable to use high frequency heating in the solid-solution treatment.
FIG. 5 will be explained in more detail below. That is, FIG. 5 shows a relationship between crystal grain size in the non-magnetized region obtained by local solid-solution treatment of the ferromagnetized part by high frequency heating and changes in the relative magnetic permeability xcexc after cooling to and retaining the non-magnetized region at xe2x88x9240xc2x0 C. As already mentioned above, it has been found that the relative magnetic permeability xcexc will not exceed 1.2 even after having retained the non-magnetized region at xe2x88x9240xc2x0 C. by selecting the heating conditions so that the crystal grain size can be kept not more than 30 xcexcm.
The present inventors have found the desired conditions for metallic members applicable to desired composite magnetic members, as mentioned above, but have not yet found a fully satisfactory process for producing a desired composite magnetic member. For example, the present inventors tried to make cup-shaped members 10 shown in FIG. 10C by the conventional continuous press drawing work, but have found that the magnetic flux density B4000 of not less than 0.3 T, as desired in the present invention, could not constantly be obtained only by conducting such a continuous press drawing work. As a result of further investigations, the present inventors have attributed the following fact to a failure to obtain the desired magnetic flux density B4000.
Explanation will be made, referring to FIG. 6, which shows a relationship between a degree of working in working steps and a working temperature of the metallic member under plastic working.
Once a strain is given to the metallic member, the working temperature of the member under plastic working will readily reach the Md point, a limit temperature for the transformation of austenite structure showing non-magnetic properties to martensite structure showing ferromagnetic properties due to heat generation during the plastic working. The present inventors have found that the further working over a point X corresponding to the Md point will be an over-working xcex1 that gives a strain that does not contribute any more the generation of martensite structure, and thus working only up to the point X can give an effective strain, though the over working xcex1 has a possibility for ferromagnetization.
Thus, the present inventors have conceived that the above-mentioned problem can be solved by giving a strain divisionally, thereby suppressing or reducing the heat generation during the working to a minimum, and that further ferromagnetization can be attained by cooling the member to not more than the room temperature to remove the heat generated during the divisional plastic working in advance to a succeeding divisional working step and then conducting the succeeding plastic working step to give a strain to the member.
That is, by conducting the plastic working such as drawing and ironing in a divisional manner, for example, at as many stages as possible, to obtain a metastable austenite stainless steel structure, it can be optimized to give a strain in the plastic working, as shown by a zigzag line B in FIG. 6, and the heat generation due to the plastic working can be suppressed thereby.
In FIG. 6, the plastic working shown by zigzag line B is conducted by dividing the conventional single working step to three stages {circle around (1)}, {circle around (2)} and {circle around (3)}.
By conducting the plastic working at a plurality of stages in this manner, the plastic working can be performed to the desired final degree of working while maintaining the working temperature below the Md point and thus a satisfactory ferromagnetic property can be given to the member.
Furthermore, the plastic working to give a strain can be carried out after cooling the member in advance. By cooling the member in advance, the working temperature of the member can be kept lower than the Md point even at the final degree of working, as shown by line C in FIG. 6, and the ferromagnetization level of the member, for example, B4000, can be readily made not less than 0.3 T thereby. That is, the member is cooled to an extremely low temperature such as down to xe2x88x92196xc2x0 C. to improve the ferromagnetization level and remove the heat generated during the plastic working. By this cooling treatment, the target ferromagnetization level such as a magnetic flux density B4000 of not less than 0.3 T can be attained without any increased number of working stages, that is, with a higher working efficiency. The working temperature of the member at the individual working stages should be not more than 100xc2x0 C. for the following reasons.
FIG. 7 shows a relationship between a working temperature of metallic member and a martensite proportion (%).
The present inventors investigated a relationship between a strain-giving rate and an increase in the working temperature of the member by tension tests. Then, the present inventors conducted a tension test of metastable austenite stainless steel in a thermostat tank at a strain-giving rate of 1 mm/min at which the heat generation due to the plastic working could be disregarded. As a result, it was found that the no more martensite structure was generated at 100xc2x0 C. or higher, as shown in FIG. 7. That is, the proportion of generated martensite structure is 10% or less at 100xc2x0 C. or higher. Thus, the desired magnetic characteristics could be obtained by using a working temperature of not more than 100xc2x0 C. in the plastic working of the member.
The present inventors have made further studies and have found that stress corrosion cracking can be prevented by applying an ironing work of 10% or more to the metallic member after the drawing work.
FIG. 8 shows a relationship between a degree of ironing work and changes in residual stress.
The main factor for causing stress corrosion crackings is said to be a residual tensile stress occurring along the circumferential direction (see FIG. 9), generated by the drawing work, and the residual tensile stress can be considerably reduced by the ironing work. As shown in FIG. 8, the residual stress can enter into a region causing no more residual stress cracking at a degree of ironing work of 10%, and can be completely changed in a residual compression strain, contrary to expectation, at a degree of ironing work of 20% or more. Samples of an ironed member were evaluated by dipping in an aqueous 42% magnesium chloride solution. It was found by this test that no stress corrosion cracking occurred on the samples subjected to ironing work with a degree of ironing work of 10% or more as shown in Table 1. The ironing work is also a very effective means for giving a strain to attain ferromagnetization, and thus is one of steps for ferromagnetization.
In summary, according to a first aspect of the present invention there is provided a composite magnetic member which comprises a metallic member comprising not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% No, not more than 1% Nb, and the balance being Fe and inevitable impurities, where
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19, wherein % is by weight, the metallic member being ferromagnetized by cold working, part of the ferromagnetized member being made by local solid-solution treatment to have crystal grain sizes of not more than 30 xcexcm, thereby making the locally non-magnetized part have a relative magnetic permeability xcexc of not more than 1.2 at a temperature as low as xe2x88x9240xc2x0 C.
It is preferable, after the ferromagnetization by cold working or after local non-magnetization of part of the ferromagnetized member by local heating, to further conduct a stress relieving annealing at a temperature of not higher than 500xc2x0 C. By conducting the stress relieving annealing, the ferromagnetization can be further intensified. The stress relieving annealing is a treatment to improve the magnetic characteristics by removing plastic strains given to the member by cold working.
According to a second aspect of the present invention, there is provided a process for producing a composite magnetic member, which comprises ferromagnetizing a metallic member comprising not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% Mo, not more than 1% Nb, and the balance being Fe and inevitable impurities, where
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19%, wherein % is by weight, by cold working, and then subjecting part of the ferromagnetized member to local solid-solution treatment within 10 seconds without melting the part, thereby making crystal grain sizes of the part not more than 30 xcexcm and making the thus no-magnetized part have a relative magnetic permeability xcexc of not more than 1.2 at a temperature as low as xe2x88x9240xc2x0 C. It is preferable to conduct the solid-solubilization treatment within 2 seconds.
According to a third aspect of the present invention there is provided a process for producing a composite magnetic member, which comprises subjecting a metallic member comprising not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% Mo, not more than 1% Nb, and the balance being Fe and inevitable impurities, where
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19%, wherein % is by weight, to a drawing step and an ironing step, thereby ferromagnetizing the member, and then non-magnetizing part of the ferromagnetized member, thereby making the non-magnetized part have a relative magnetic permeability xcexc not more than 1.2 at a temperature as low as xe2x88x9240xc2x0 C.
According to a fourth aspect of the present invention, there is provided a process for producing a composite magnetic member, which comprises subjecting a metallic member comprising not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% Mo, not more than 1% Nb, and the balance being Fe and inevitable impurities, where
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19%, wherein % is by weight, to a strain-giving working step at a plurality of stages while controlling the working temperature of the individual working stages to not more than 100xc2x0 C., thereby making the member into a ferromagnetized member having a magnetic flux density B4000 of not less than 0.3 T, and then subjecting part of the ferromagnetized member to local solid-solution treatment within 10 seconds, thereby making crystal grain sizes of the solid-solution-treated part not more than 30 xcexcm.
According to a fifth aspect of the present invention, there is provided a process for producing a composite magnetic member, which comprises cooling a metallic member comprising not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% Mo, not more than 1% Nb, and the balance being Fe and inevitable impurities, where
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19%, wherein % is by weight, to a temperature of not more than room temperature, then subjecting the member to a strain-giving working step, while controlling working temperature to not more than 100xc2x0 C., thereby making the member into a ferromagnetized member having a magnetic flux density B4000 of not less than 0.3 T, and subjecting part of the ferromagnetized member to local solid-solution treatment within 10 seconds, thereby making crystal grain sizes of the solid-solution-treated part not more than 30 xcexcm.
According to a sixth aspect of the present invention, there is provided a process for producing a composite magnetic member, which comprises subjecting a metallic member comprising not more than 0.6% C, 12 to 19% Cr, 6 to 12% Ni, not more than 2% Mn, not more than 2% Mo, not more than 1% Nb, and the balance being Fe and inevitable impurities, where
Hirayama""s equivalent H eq=[Ni %]+1.05 [Mn %]+0.65 [Cr %]+0.35 [Si %]+12.6 [C %] is 20 to 23%;
Nickel equivalent Ni eq=[Ni %]+30 [C %]+0.5 [Mn %] is 9 to 12%, and
Chromium equivalent Cr eq=[Cr %]+[Mo %]+1.5 [Si %]+0.5 [Nb %] is 16 to 19%, wherein % is by weight, to a strain-giving working step at a plurality of stages while controlling the working temperature of the individual working stages to not more than 100xc2x0 C., then subjecting the member to ironing work at a degree of ironing of not less than 10%, thereby making the member into a ferromagnetized member having a magnetic flux density B4000 of not less than 0.3 T, and then subjecting part of the ferromagnetized member to local solid-solution treatment within 10 seconds, thereby making the locally solid-solution-treated part have crystal grain sizes of not more than 30 xcexcm. After the solid-solution treatment, the resulting member may be subjected to not working at a temperature of not less than 100xc2x0 C, thereby forming the member into a desired shape.
According to a seventh aspect of the present invention there is provided an electromagnetic valve, which comprises a movable iron core provided slidably in a magnetic circuit formed by excitation of a coil, the movable iron core being adapted to open or shut a fluid passage by sliding caused by the excitation of the coil, and a support member with a slide hole through which the movable iron core is inserted slidably, at least one part of the support member being provided in the magnetic circuit, the support member being made from a metallic member comprising at least one ferromagnetized part and at least one non-magnetized part, as continuously and integrally formed, the non-magnetized part having a span of not less than 1 mm wide.
According to an eighth aspect of the present invention there is provided an electromagnetic valve, which comprises a movable iron core provided slidably in a magnetic circuit formed by excitation of a coil, the movable iron core being adapted to open or shut a fluid passage by sliding caused by the excitation of the coil, and a support member with a hole through which the movable iron core is inserted slidably, at least one part of the support member being provided in the magnetic circuit, the support member being made from a metallic member comprising at least one ferromagnetized part and at least one non-magnetized part, as continuously and integrally formed, and the non-magnetized part surrounding at least the lower end of the movable iron core.
In the first to third aspects of the present invention a remarkable composite magnetic member, whose non-magnetized part is never converted to a ferromagnetized part, even when exposed to a severe temperature condition, can be provided on the basis of the novel findings shown in FIGS. 1 to 5.
In the first to sixth aspects of the present invention a composite magnetic member having at least one ferromagnetized part and at least one non-magnetized part, as continuously and integrally formed, can be produced quite easily, on the basis of the novel findings shown in FIGS. 1 to 8.
In the seventh aspect of the present invention, a support member having at least one ferromagnetized part and at least one non-magnetized part, as continuously and integrally formed, is used in an electromagnetic valve and a movable iron core can be stably driven by using the non-magnetized part having a span of not less than 1 mm wide.
In the eighth aspect of the present invention the support member, whose non-magnetized part is made to surround the lower end of the movable iron core, is provided and thus the movable iron core can be more stably driven.